In recent years, electric power generation systems utilizing recyclable energy, such as wind power and solar light, attract attention in view of greenhouse effect gas reduction.
For example, Non-Patent Literature 1-3 describe technology relating to wind power generation. Wind power generation rotates a wind turbine by wind to drive an electric power generator to generate electric power. In other words, it converts wind energy into rotational energy and extracts it as electrical energy. A wind power generation system is generally structured such that a tower has an upper portion provided with a nacelle having a horizontal axis wind turbine (a wind turbine having a rotary shaft generally parallel to the wind's direction) attached thereto. The nacelle has accommodated therein a speed up gear which accelerates and thus outputs the rotational speed of the shaft of the wind turbine, and an electric power generator driven by the output of the speed up gear. The speed up gear raises the rotational speed of the wind turbine to the rotational speed of the electric power generator (for example 1:100), and has a gear box incorporated therein.
In these days, for reduced electric power generation costs, there is a tendency to increase a wind turbine (or a wind power generation system) in size, and a wind power generation system of 5 MW with a wind turbine having a diameter of 120 m or larger is put in practical use. Such a large-sized wind power generation system is huge and a heavy load, and accordingly, it is built on the sea for reasons of construction in many cases.
Furthermore, wind power generation provides a varying power generation output (or generates electric power in a varying amount) as wind power varies, and accordingly, an electric power storage system is also provided for a wind power generation system to store unstable electric power in a storage battery to smooth an output.
On the other hand, for example Non-Patent Literature 4 describes technology relating to solar thermal power generation. Solar thermal power generation collects solar heat and changes it into thermal energy and uses the thermal energy to generate steam to rotate a turbine to drive an electric power generator to generate electric power. In other words, it converts solar energy into thermal energy, and extracts it as electrical energy. A solar thermal power generation system that is put in practical use is of a tower system, for example. This is a system which collects solar light to a solar collector provided at an upper portion of a tower and utilizes its heat to generate steam which is in turn delivered to a turbine provided at a lower portion of the tower to rotate the turbine to drive an electric power generator to generate electric power (see Non-Patent Literature 4, FIG. 3).
Solar thermal power generation also provides an output varying with weather, time and the like, and accordingly, for stable electric power generation, a thermal storage system capable of storing heat in a heat accumulator and extracting heat required for generating electric power is provided for a solar thermal power generation system.